if condition

Shell Programming and Scripting
1

Hi

how to write this:

if [ $x different from these 2 strings: 'A' or 'B' ]
then
usage
fi

thx

2 
if [[ $x != "A" || $x != "B" ]]

more here Other Comparison Operators
and Nested if/then Condition Tests

Please use code tags.

3

hi

...
echo $x
if [[ "$x" != "A" || "$x" != "B" ]]
then
fct
else
echo OK
fi
...

the output is:

A
fct output (another echo)

any idea?

4 
The Boolean needs to be: (NOT = A) AND (NOT = B).
For example:

#!/bin/ksh
x="$1"
#
echo $x
if [[ ! "$x" = "A" && ! "$x" = "B" ]]
then
        echo fct
else
        echo OK
fi

However this is brain damage to follow in scripts.
IMHO a case statement is easier to follow for basic validation.

#!/bin/ksh
x="$1"
#
case "${x}" in
        "A"|"B")
                echo "Valid value: ${x}"
                continue
                ;;
        *)
                echo "Invalid value: ${x}"
                exit
                ;;
esac